The field of the invention is the preparation of 2,2-dimethyl-1,3-propanediol from hydroxy pivalic aldehyde.
Hydroxy pivalic aldehyde is a preliminary state in the production of 2,2-dimethyl-1,3-propanediol, otherwise known as neopentylglycol. Hydroxy pivalic anhydride is reacted both by catalytic reduction and by the Cannizzaro reaction of the aldehyde to form 2,2-dimethyl-1,3-propanediol. The catalysts used in the hydrogenation include, besides Ni, catalysts as disclosed in U.S. Pat. No. 2,400,724, also copper chromites as disclosed in British Pat. No. 1,017,618.
In addition to alkali metal compounds, further alkali earth metal compounds and amines have been described as useful in the aldolization of isobutyraldehyde and formaldehyde.
The salt contents of organic acids is of utmost significance in preparing pure 2,2-dimethyl-1,3-propanediol (neopentylglycol) by distillation. On account of the presence of these salts, the required high temperature of distillation entails dissociation, or resinification of the desired diol. On the one hand, this means substantial losses of product and on the other hand, only an impure diol is obtained. The presence of such salts illustratively alkali/alkali earth/ammonium formiates, isobutyrates or hydroxypivalates can be explained for instance by the Cannizzaro reaction or the presence of traces of oxygen during aldolization.
The state of the art of removing salts from hydrogenation outputs may be ascertained by reference to U.S. Pat. No. 2,865,819; West German Patent Publications No. 967,552; 1,052,383 and 2,045,668 and Japanese Patent No. 69/10767 the disclosures of which are incorporated herein by reference.
The state of the art of aldolization of isobutyraldehyde and formaldehyde to hydroxy pivalic aldehyde and the preparation of neopentylglycol from hydroxy pivalic aldehyde may be ascertained by reference to U.S. Pat. No. 4,250,337 the disclosure of which is incorporated herein by reference.
In the method of Japanese Patent No. 69/10767, the use of extractants such as di-n-butylether is recommended. Also, pretreatment of the hydrogenation output using a thin-film-evaporator is recommended to separate salts and substances of higher boiling points accumulating during synthesis. In U.S. Pat. No. 2,865,819, the salts are removed by adding water and Tetralin and subsequent multi-stage reprocessing by distillation. In West German Published Application No. 1,052,383, polyvalent alcohols are recovered from their aqueous, salt-containing solutions by a quasi "steam distillation" using a thin film evaporator. The use of phosphoric acid is described in West German Patent No. 2,045,668. Again, the use of ion exchangers to treat the "raw product" is described in West German Patent No. 967,552.
Most of the procedures discussed are quite costly because, besides a multistage distillation of the raw product, illustratively also drying and crystallization stages must be carried out or a final aftertreatment with ion exchangers is required. Even the treatment with phosphoric acid according to West German Patent No. 2,045,668 does not permit processing the crude 2,2-dimethyl-1,3-propanediol solution which is extensively free from dissociation. While Applicant's own lab procedures show that the dissociation rate can be decreased, it remains nevertheless significant.
Therefore, a long felt need exists to create a process whereby 2,2-dimethyl-1,3-propanediol is isolated from the raw product in simple and salt free manner without significant dissociation losses.